The new U.S. Environmental Protection Agency (EPA) issued the Mercury and Air Toxics Standards (MATS) regulations stating that existing coal-fired power plants must achieve ≤ 0.002 lb/MMBtu emissions of hydrogen chloride (HC1). EPA Method 26A is the approved test method for halides, including HC1, but this method can skew the HC1 results high in the presence of ammonium chloride (NH_4C1). At Detroit Edison's Monroe Power Plant Units 3 and 4, it was discovered that a high ammonia slip from a selective catalytic reduction (SCR) system resulted in the formation of ammonium chloride. The fine ammonium chloride particulate escapes complete capture in the wet flue gas desulfurization (FGD) system, and can be subsequently detected by EPA Method 26A and reported as HC1. In some cases, this can result in HC1 values being erroneously reported higher than permitted limits. Stack testing was completed using Fourier transform infrared (FTIR) spectrometry at various operating conditions to understand the formation of ammonium chloride in the system and yield the correct HC1 emissions results.
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